Projections of declining surface-water availability for the southwestern United States


Global warming driven by rising greenhouse-gas concentrations is expected to cause wet regions of the tropics and mid to high latitudes to get wetter and subtropical dry regions to get drier and expand polewards1,2,3,4. Over southwest North America, models project a steady drop in precipitation minus evapotranspiration, PE, the net flux of water at the land surface5,6,7, leading to, for example, a decline in Colorado River flow8,9,10,11. This would cause widespread and important social and ecological consequences12,13,14. Here, using new simulations from the Coupled Model Intercomparison Project Five, to be assessed in Intergovernmental Panel on Climate Change Assessment Report Five, we extend previous work by examining changes in P, E, runoff and soil moisture by season and for three different water resource regions. Focusing on the near future, 2021–2040, the new simulations project declines in surface-water availability across the southwest that translate into reduced soil moisture and runoff in California and Nevada, the Colorado River headwaters and Texas.

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Figure 1: The average across the 16 CMIP5 models of the change in P and PE for 2021–2040 minus 1951–2000, using the RCP85 emissions scenario for the future and the simulations with historical forcing for the past.
Figure 2: The difference in PE relative to 1951–2000 for two-decade periods of the present century for the California and Nevada region, the Colorado River headwaters region and the Texas region.
Figure 3: Changes by season in P, E, runoff and soil moisture for 2021–2040 under the RCP85 emissions scenario minus 1951–2000 using the 16 model CMIP5 ensemble.


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This work was supported by NOAA awards NA08OAR4320912 and NA10OAR4310137 and NSF award AGS-08-04107. The comments of the wider Global Decadal Hydroclimate Variability and Change (GloDecH) group at Lamont are greatly appreciated.

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R.S., M.T. and B.C. conceived the analyses. R.S. wrote the paper with input from all authors. C.L., H.L., J.N. and N.N. performed analyses on the model data. C.L. and J.N. prepared the figures.

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Correspondence to Richard Seager.

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Seager, R., Ting, M., Li, C. et al. Projections of declining surface-water availability for the southwestern United States. Nature Clim Change 3, 482–486 (2013).

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